Process for the preparation of styrenes

ABSTRACT

Styrene or substituted styrenes are produced by a process comprising the gas phase dehydration of 1-phenyl ethanol or substituted 1-phenyl ethanol in the presence of a solid acidic catalyst comprising a zeolite and a binder material, wherein the weight ratio of zeolite to binder is in the range of from 1:99 to 90:10 and wherein the following relation applies: 0&lt;K&lt;5 with K=V/S×[(Pz×fz)+(Pb×fb)] ½ , wherein: V/S is the volume/surface ratio of the catalyst used in mm; fz is the weight fraction of zeolite present in the catalyst in grams zeolite per gram catalyst; fb is the weight fraction of binder present in the catalyst in grams binder per gram catalyst; pz is the intrinsic productivity of zeolite expressed as grams styrene produced per gram of the zeolite per hour, as measured for pure zeolite samples of small particle size (i.e., &lt;0.1 mm) at the temperature applied in gas phase dehydration and at a conversion of 1-phenyl ethanol into styrene below 80%; and Pb is the intrinsic productivity of the binder expressed as grams styrene produced per gram of binder per hour, as measured for pure binder samples of small particle size (i.e., &lt;0.1 mm) under the same conditions as used for determining Pz.

The present invention relates to a process for the preparation ofstyrene or substituted styrenes, more specifically to such a processcomprising the gas phase dehydration of 1-phenyl ethanol or substituted1-phenyl ethanols.

Within the further context of the present application the term“substituted styrenes” refers to vinyl aromatic compounds of the generalformula

Ar—CR═CH₂,

wherein Ar is a phenyl, tolyl or xylyl group and R is H or a methylgroup. When referring to “styrene” in the present application, thesesubstituted styrenes are also included, unless indicated otherwise.Similarly, the term “substituted 1-phenyl ethanols” refers to aromaticalcohols of the general formula

Ar—C(R)(CH₃)—OH

wherein Ar and R are as defined above. When referring to “1-phenylethanol”, these substituted 1-phenyl ethanols are also included, unlessindicated otherwise.

A commonly known method for manufacturing styrene is the coproduction ofpropylene oxide and styrene starting from ethylbenzene (a StyreneMonomer/Propylene Oxide or SM/PO process). In general such processinvolves the steps of (i) reacting ethylbenzene with oxygen or air toform ethylbenzene hydroperoxide, (ii) reacting the ethylbenzenehydroperoxide thus obtained with propene in the presence of anepoxidation catalyst to yield propylene oxide and 1-phenyl ethanol, and(iii) converting the 1-phenyl ethanol into styrene by dehydration usinga suitable dehydration catalyst. The present invention particularlyfocuses on the last step, i.e. the dehydration of 1-phenyl ethanol toyield styrene.

Step (iii) of the process described above, i.e. the production ofstyrene by dehydrating 1-phenyl ethanol, can be carried out in differentways as is well known in the art. In general, the dehydration can becarried out in the gas phase or in the liquid phase in the presence of adehydration catalyst. Suitable dehydration catalysts are known andinclude for instance acidic materials like alumina, alkali alumina,aluminium silicates and H-type synthetic zeolites. Dehydrationconditions are also well known and usually include reaction temperaturesof 50-205° C., typically 100-200° C., for liquid phase dehydration and210-320° C., typically 280-310° C., for gas phase dehydration. Pressuresusually range from 0.1 to 10 bar.

In GB-A-2,176,801 the liquid-phase dehydration of an aromatic alcoholinto an aromatic vinyl compound is described, wherein the dehydration iscarried out at elevated temperature in the presence of a solid acidcatalyst. Aluminium silicate and H-type synthetic zeolites are mentionedas suitable catalysts, but no further details as to the properties ofthese materials is given.

In Takahashi et al., The Canadian Journal of Chemical Engineering, Sol.66, June 1988, pp. 433-437, a process for the liquid phase dehydrationof 1-phenyl ethanol into styrene is described using various types ofacidic catalysts. The catalysts used include silica-alumina, Y typezeolites, mordenites, H-ZSM-5 and several aluminas, all used in the formof crushed particles of 24-32 mesh (corresponding with 0.5 to 0.7 mm).This publication concludes that when the concentration of effective acidsites on the catalyst increases, the dehydration reaction rateincreases, but the styrene selectivity decreases. A certain aluminacatalyst was found to provide the best balance between reaction rate andstyrene selectivity.

In JP-A-61/72727 the gas-phase dehydration of 1-phenyl ethanol intostyrene is described, wherein a zeolite is used as the dehydrationcatalyst. The patent application does not give any further details as tothe types and properties of suitable zeolites, except that in theworking examples OSZ-250, a H-Y-type zeolite, is used in the form ofcrushed particles having a size of 32-60 mesh (corresponding with0.25-0.50 mm). In the working example the feed solely consisted of1-phenyl ethanol without other compounds being present.

The present invention aims to provide an effective dehydration processfor converting 1-phenyl ethanol into styrene, which process can also beused in the dehydration step of a commercial SM/PO process. In such aprocess the feed to the dehydration section will not only contain1-phenyl ethanol, but also substantial amounts of other compounds formedin the preceding sections. Examples of such compounds are 2-phenylethanol, methyl phenyl ketone, some styrene monomer, ethylbenzene andwater.

It has been found that 1-phenyl ethanol either as such or in a processstream in an SM/PO process can be very effectively converted intostyrene in a gas phase dehydration process by selecting a zeoliticcatalyst meeting certain specific requirements.

Accordingly, the present invention relates to a process for thepreparation of styrene or substituted styrenes comprising the gas phasedehydration of 1-phenyl ethanol or substituted 1-phenyl ethanol in thepresence of a solid acidic catalyst comprising a zeolite and a bindermaterial, wherein weight ratio of zeolite to binder is in the range offrom 1:99 to 90:10 and wherein the following relation applies:

0<K<5  (1)

with:

K=V/S*[(Pz*fz)+(Pb*fb)]^(½)  (2)

wherein:

V/S is the volume/surface ratio of the catalyst used in mm;

fz is the weight fraction of zeolite present in the catalyst in gramszeolite per gram catalyst;

fb is the weight fraction of binder present in the catalyst in gramsbinder per gram catalyst;

Pz is the intrinsic productivity of the zeolite expressed as gramsstyrene produced per gram of zeolite per hour, as measured for purezeolite samples of small particle size (i.e. <0.1 mm) at the temperatureapplied in gas phase dehydration and at a conversion of 1-phenyl ethanolinto styrene below 80%; and

Pb is the intrinsic productivity of the binder expressed as gramsstyrene produced per gram of binder per hour, as measured for purebinder samples of small particle size (i.e. <0.1 mm) under the sameconditions as used for determining Pz.

The catalyst to be used comprises zeolite and binder in a weight ratioof zeolite to binder of from 1:99 to 90:10, preferably of from 3:97 to35:65. Suitable binder materials include inorganic oxides like silica,alumina, boria, zirconia, titania and silica-alumina as well as organicmaterials like carbon or polymers. Of these, the substantially inertbinder materials silica and alumina are preferred. The zeolite to beused in principle may be any zeolite having sufficient acidity tocatalyse the dehydration of 1-phenyl ethanol. Suitable zeolites, then,include H-ZSM-5, H-ZSM-23, H-mordenite, H-Y-zeolite and beta-zeolite,but also silica-alumina phosphate molecular sieve materials, such asSAPO-34. However, other acidic zeolitic materials may be applied aswell.

The catalyst to be used must meet very specific requirements as regardsparticle size, outer surface and zeolite content. These requirements aresummarised in equations (1) and (2):

0<K<5  (1)

with:

K=V/S*[(Pz*fz)+(Pb*fb)]^(½)  (2)

wherein V/S, Pz, Pb, fz and fb have the meaning as indicated above. Thequotient of volume V (in mm³) and outer surface S (in mm²) is expressedin mm and is a measure for the particle size and its shape. Forspherical catalyst particles, V/S is ⅙ of the particle diameter. Forcylindrical catalyst particles V/S is ¼ of the particle diameter. Forcatalyst particles shaped as trilobes, stars, quadrulobes, wokkels andthe like, the ratio V/S will be smaller than ¼ of the outer diameter ofthe enclosing cylinder. It has been found advantageous to select V/S,Pz, Fb, fz and fb such that K has a value of less than 2, preferably ofless than 0.5 and most preferably of less than 0.2.

The weight fractions of zeolite (fz) and binder (fb) Indicate theamounts of zeolite and binder in grams per gram of catalyst. The sum offz and fb is equal to 1, i.e. the catalyst consists of zeolite andbinder. The productivities Pz and Pb in fact indicate the dehydrationactivity of the pure zeolite and pure binder, respectively. For thepurpose of the present invention it is preferred that the binder issubstantially inert, so that Pb=0. As a result, the following relationapplies:

 K=V/S*(Pz*fz)^(½)  (3)

The conditions under which the dehydration is carried out may varywithin wide limits, but should anyhow be such that the 1-phenyl ethanolis in the gas phase. At atmospheric pressure this implies that thereaction temperature should be higher than the boiling temperature of1-phenyl ethanol, which is 203-204° C. At subatmospheric conditions,however, the reaction temperature may be lower. In general, the gasphase dehydration is suitably carried out at a temperature in the rangeof from 205 to 300° C., preferably 210 to 250° C., at a pressure of from0.5 to 5 bar.

The process according to the present invention can be carried out indifferent operational modes in terms of the way in which the catalyst isused. In one embodiment of the present invention the catalyst is used inthe form of particles having an average particle size of at least 0.5mm, preferably from 1 to 10 mm, more preferably from 1.5 to 5 mm, in apacked fixed bed. Such relatively large particle sizes are preferred tokeep the pressure drop within the reactor at an acceptable level. Inthis mode of operation the catalyst particles are randomly packed into abed over which the feed comprising 1-phenyl ethanol is passed upwardlyor downwardly. The catalyst particles may have any desired shapeincluding spherical, (hollow) cylindrical, trilobe, star-shaped,pellet-shaped etc. In another embodiment of the present invention thecatalyst is used in the form of particles having an average particlesize of 0.5 mm or less, preferably from 0.02 to 0.1 mm, in a fluidisedbed. In this mode of operation spherical catalyst particles are normallyapplied, so that the ratio V/S equals ⅙ of the diameter of the catalystparticles. Since the catalyst particles are free flowing and hence areexposed to relatively severe mechanical forces, a certain minimum amountof binder material should be present to give the catalyst particlessufficient strength. Preferred binder contents are 20% by weight ormore, more preferably at least 30% by weight. The gaseous feed entersthe fluidised bed reactor at the bottom at a certain velocity, thushelping to keep the catalyst bed in its fluidised state, and thestyrene-containing product leaves the reactor at the top.

In a still further embodiment of the present invention the catalyst isapplied as a layered catalyst, which is as a thin layer on either smallsupport particles or on a monolithic support or a structured packing. Inthese forms the catalyst is most suitably applied in a fixed bedoperation. The coated catalyst particles, however, could also be appliedin a fluidised bed operation, if the particles are sufficiently small(i.e. <100 μm). In general, monolithic catalysts are continuous, unitarystructures containing many narrow, parallel straight or zigzag passages.Catalytically active ingredients are distributed uniformly in a porouslayer deposited on the walls of the channels in the monolithicstructure. A frequently applied monolithic structure is the honeycombstructure. The essence of monolithic catalysts is the very thin layers,in which internal diffusion resistance is small. A structured packing isan open cross-flow structure, which can serve as a catalyst carrier byapplying a thin layer of catalytically active material on the walls ofthe channels. Such structured packings are for instance available fromSulzer Chemtech. An example of a structured packing is a foam containingchannels. For all layered catalysts (coated particles, monolithicsupports and structured packings) the thickness of the applied catalystlayer will usually vary between 1 and 100 μm, more suitably 1 and 50 μm.The V/S ratio in this case will be about equal to the layer thicknessassuming that the half of the total surface bound to the support is notaccessible for the reactant gas.

The invention is further illustrated by the following example withoutrestricting the scope of the invention to the particular embodimentsillustrated in this example.

EXAMPLE

The experiments were carried out in a stainless steel reactor (13 mminternal diameter; 30 cm length) equipped with an internal thermowell(0.5 outer diameter). The feed was passed downwardly through thereactor. The catalyst particles used were diluted with glass beads (2 mmdiameter) prior to filling the central segment of the reactor. The feedline was traced to the reactor temperature to allow the feed tovaporise. The product was collected and analysed by means of gaschromatography. The feed consisted of:

82% by weight of 1-phenyl ethanol

5% by weight 2-phenyl ethanol

11% by weight methyl phenyl ketone

1-2% by weight of water and

the balance up to 100% by weight of styrene plus ethyl benzene.

The catalyst used was based on H-ZSM-5 zeolite, which was extruded withSiO₂ into trilobes of 1.6 mm outer diameter. Two batches were prepared:one with 20% by weight zeolite and one with 80% by weight zeolite. Theextruded catalyst was also tested in the form of crushed particles ofabout 0.2 mm.

The reactor was loaded with a sufficient amount of catalyst to haveabout 0.5 grams of zeolite in the reactor. The catalyst was heated undera flow of nitrogen, initially rapidly up to 80° C., then within 2 hoursto 120° C. and subsequently rapidly up to the reaction temperature of220° C., at which temperature the catalyst was kept for 2 hours. Then,the feed was introduced into the reactor and the catalyst was contactedwith the vaporised feed at a rate of 18 g/h (corresponding with a weighthourly space velocity of 30 grams 1-phenyl ethanol per gram zeolite perhour) and atmospheric pressure for several days.

The productivity Pz of the zeolite was determined by running the purezeolite powder diluted in glass beads at 220° C. and at a 1-phenylethanol conversion of approximately 55%. The Pz had a value of 5 gstyrene/g zeolite/h.

The results are indicated in Table I. The abbreviations D, Conv. andSel. refer to catalyst particle diameter, conversion and selectivity,respectively. The conversion is calculated on the basis of the carboncontent C of the feed and of the unconverted feed leaving the reactor:${Conversion} = {\frac{{C({feed})} - {C\left( {{unconverted}\quad {feed}} \right)}}{C({feed})} \times 100\quad \%}$

The carbon content of the unconverted feed is the difference between thetotal carbon content of the product stream that leaves the reactor andthe C of the styrene formed.

The selectivity is calculated on the basis of the carbon content of thestyrene formed and the carbon content of the feed:${Selectivity} = {\frac{C({styrene})}{C({feed})} \times 100\quad \%}$

TABLE I Results Run D fz V/S Time Conv. Sel. No. (mm) (g/g) (mm) K (h)(%) (%) 1 0.2 0.2 0.033 0.03 5 95 98 50 92 97 100 90 98 2 0.2 0.6 0.0330.05 5 95 90 50 85 93 100 81 92 3 1.6 0.2 0.400 0.38 5 95 95 50 80 94100 65 92 4 1.6 0.6 0.400 0.66 5 60 75 50 52 80 100 45 82

From Table I it can be seen that the selectivity is high and stable forcatalysts having a K of less than 0.5 (runs Nos. 1-3). The catalyst witha K of more than 0.5 is still performing adequately, but shows asomewhat lower selectivity which is also less stable. The conversion forthe catalysts used in runs Nos. 1-3 is also somewhat higher than theconversion for the catalyst used in run No. 4, although the latter isstill sufficiently high.

Comparative Example

Run No. 3 was repeated, but with a liquid in stead of a vaporous feed.Two runs of 48 hours each were carried out, one at 120° C. (run No. 5)and one at 170° C. (run No. 6), at a space velocity of 10 g 1-phenylethanol/g zeolite/h.

It was found that in both runs the conversion was higher than 80%, butthe selectivity did not exceed 30% (run No. 5) and 50% (run No. 6).

Hence, the comparative examples demonstrate that the process accordingto the present invention must be a gas phase process.

What is claimed is:
 1. Process for substituted styrenes comprising thegas phase dehydration of 1-phenyl ethanol or substituted 1-phenylethanol in the presence of a solid acidic catalyst comprising a zeoliteand a binder material, wherein the weight ratio of zeolite to binder isin the range of from 1:99 to 90:10 and wherein the following relationapplies: 0<K<5  (1) with: K=V/S*[(Pz*fz)+(Pb*fb)]^(½)  (2) wherein: V/Sis the volume/surface ratio of the catalyst used in mm; fz is the weightfraction of zeolite present in the catalyst in grams zeolite per gramcatalyst; fb is the weight fraction of binder present in the catalyst ingrams binder per gram catalyst; Pz is the intrinsic productivity of thezeolite expressed in as grams styrene produced per gram of zeolite perhour, as measured for pure zeolite samples of small particle size at thetemperature applied in the gas phase dehydration and at a coversion of1-phenyl ethanol into styrene below 80%; and Pb is the intrinsicproductivity of the binder expressed as grams styrene produced per gramof binder per hour, as measured for pure binder samples of smallparticle size under the same conditions as used for determining Pz. 2.Process according to claim 1, wherein K has a value between 0 and
 2. 3.Process according to claim 1 wherein the intrinsic productivity of thebinder, Pb, is essentially zero, so that: K+V/S*(Pz*fz)^(½) wherein V/S,Pz and fz are as defined in claim
 1. 4. Process according to claim 2,wherein the weight ratio of zeolite to binder is in the range of from3:97 to 35:65.
 5. Process according to claim 4, wherein the binder issilica or alimina.
 6. Process according to claim 1, wherein thetemperature at which the gas phase dehydration is carried out is in therange of from 205 to 300° C., at a pressure of from 0.5 to 5 bar. 7.Process according to claim 1 wherein the zeolite is H-ZSM-5, H-ZSM-23,H-mordenite, H-Y-zeolite or a silica-alumina phosphate.
 8. Processaccording to claim 1, wherein the catalyst is used in the form ofparticles having an average particle size of at least 0.5 mm in a packedfixed bed.
 9. Process according to claim 4, wherein the catalyst is usedin the form of particles having an average particle size of 0.5 mm orless and in a fluidized bed.
 10. Process according to claim 4, whereinthe catalyst is applied as a coating on a monolithic support or astructured packing in a fixed bed operation.